Utility meters are devices that, among other things, measure the consumption of a utility-generated commodity, such as electrical energy, gas, or water, by a residence, factory, commercial establishment or other such facility. Utility service providers employ utility meters to track customer usage of the utility-generated commodities. Utility service providers track customer usage for many purposes, including billing and demand forecasting.
Electricity meters that measure energy consumption or power consumption typically connect between a utility power line and a load. For example, an electricity meter for a residential customer is often connected at the point at which the electrical system of the residence connects to the utility line. The meter may thereby perform measurements regarding the energy consumed by the load.
Electricity meters often include one or more electrical contacts across which the load voltage and a significant amount of current may be found. For example, meters often have blades that connect to the power line to enable the measurement of load current and load voltage from within the meter. The blades are received by the jaws of a meter mounting device of the building. Spring compression within the jaws retains the blades securely. If the meter is to be replaced or repaired, then the meter may be pulled out of the mounting device, and hence the blades out of the jaws. Although the blades and jaws are usually mechanically robust, they are nevertheless subject to wear, and possibly corrosion, particularly if the meter has been removed or replaced several times. If wear on the jaws is significant, or if the jaws have corrosion, then there is a possibility of introducing a non-trivial resistance at the jaw/blade connection, which is undesirable. In some cases, the jaw/blade connection can undesirably deteriorate to a condition in which arcing occurs.
Likewise, certain meters have switches that allow for disconnection of electrical service to a load. For example, many meters allow for remote disconnection of the load. Such switches necessarily must have substantial contacts because they carry the entire current of the load when the switch is closed. If these switches are used with some frequency, then there is a potential for degradation. Degradation of the switch contacts increases the resistance over the switch contacts. As with the meter blades and jaws, resistance creates additional power loss within the meter, and potentially arcing, both undesirable.
It is known to detect the possible deterioration of meter switch contacts by measuring the resistance and/or current through the contacts within the meter. If the resistance exceeds a threshold, then an indication of potential need for maintenance is displayed or transmitted. Such a method is taught, for example, in U.S. Pat. No. 7,683,642, issued Mar. 23, 2010. One limitation of this technique is that it can require extra elements to carry out the resistance measurement, thereby adding material cost and manufacturing complexity.
It is also known to monitor the temperature of the sockets and jaws of the meter for overheating. The detection of an overheat condition in the sockets and jaws of the meter can indicate an arcing condition, or other condition, such as increased resistance, requiring maintenance. Such a method is discussed, for example, in U.S. Pat. No. 7,513,683. This method, however, requires that the temperature sensing device be attached to a mass in thermal contact with the electrical connection. This technique, though simple, cannot be applied in meter designs where the temperature sensing device is isolated from the electrical connection by some sort of significant insulator, such as an air gap. In such meter designs, the measured temperature can be distorted to a significant extent by ambient temperature and other normal operations within the meter. As a consequence, the threshold must be high enough to avoid false positives due to other conditions causing a temperature rise in and around the meter blades.
Another known method of detecting the presence of arcing or other meter blade/socket malfunction includes monitoring RF noise within the meter. In particular, arcing between the meter blades and the meter socket causes emission of certain RF noise that may be monitored. Such a method is described in U.S. Patent Publication No. 2014/0327449. Such a solution, however, cannot readily distinguish arcing from other sources of RF noise. Thus, sometimes such a method includes monitoring other meter phenomena, such as internal temperature, so that multiple phenomena can confirm the condition. However, such a solution requires an RF receiver and has the complexity associated with monitoring multiple factors to determine if arcing is present.
Thus, a continuing need exists to detect possible issues due to deterioration of high-power switch contacts in a meter or a meter socket that can reliably and efficiently determine the presence of a maintenance issue.